The present invention relates to electric circuits for controlling the electrical components of a refrigeration unit having an active damper therein.
A commercial or domestic refrigeration unit (e.g. a refrigerator or freezer) typically includes several electrical components which must be activated in a thermostatically controlled manner to provide refrigeration. These components typically include a compressor and electric fans. The compressor compresses the cooling media upon exit from the evaporator inside of the refrigeration unit, and delivers the compressed cooling media to a condenser outside of the refrigeration unit. The electric fans are typically positioned adjacent to the evaporator inside of the unit and adjacent to the condenser outside of the unit, to effect heat transfer to/from the evaporator and condenser to the air surrounding those components. Typically, power is provided to the compressor and fans by a thermostatic switch located inside of the refrigeration unit; in essence, the thermostatic switch closes when the inside temperature exceeds a threshold, causing power to be applied simultaneously to the compressor and fans. Power continues to be applied until the inside temperature reduces and the thermostatic switch opens, at which time the compressor and fans turn off.
Many modern refrigeration units include a fresh food compartment for storing food above a freezing temperature, for example, 32.degree. F. The fresh food compartment is normally isolated from a main or freezer compartment for storing food below the freezing temperature. Often, the temperatures of the fresh food and freezing compartments can be separately controlled. To provide cooling to the fresh food compartment, the fresh food compartment is typically equipped with an active damper door, controlled by a damper motor. When the damper door is open, typically the evaporator fan is energized to move cooling air from inside of the freezer compartment into the fresh food compartment. When the damper door is closed, the fresh food compartment is isolated from the freezer compartment, and its temperature can change separately from the freezer compartment.
In a typical refrigeration unit, the fresh food compartment is equipped with its own thermostatic switch to permit thermostatic control of the temperature of the fresh food compartment. This thermostatic switch detects when the temperature of the fresh food compartment exceeds a threshold, indicating that cool air from the freezer compartment must be introduced into the fresh food compartment. When the thermostatic switch detects this condition, the thermostatic switch changes state to its "hot" condition, in which it delivers electrical power to the damper motor to open the damper, and also delivers electrical power to the evaporator fan. When the fresh food compartment cools, the thermostatic switch again changes state to its "cool" condition, in which it delivers electrical power to the damper motor to close the damper, and ceases delivery of electrical power to the evaporator fan.
Most modern refrigeration units utilize the above-described operation cycle, however, while the operating cycle in most refrigeration units is the same, there are many different mechanisms and control circuits used to control the refrigeration components in implementing that operating cycle. Further, as disclosed in U.S. Pat. No. 5,477,699, entitled "Evaporator Fan Control for a Refrigerator", many refrigeration units utilize at least three mechanically operative switches to control the operation of the damper motor and evaporation fan. Other control circuits may utilize additional switches and other components, for example, a capacitor, etc. Each additional switch or other component used to control the fresh food compartment damper increases the cost of the refrigeration control circuit, and may also reduce the reliability of the circuit as a result of the greater number of contact points.